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Abstract
Following a previous publication, the present paper reports additional results on
the effects of alcohol mobile-phase modifiers on the structure and chiral selectivity
of amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD) chiral stationary phase
(CSP). Solid-state NMR (1H/13C CPMAS) was utilized to identify and compare structural
differences in Chiralpak AD caused by the various alcohol mobile-phase modifiers,
many of which were not studied in the previous publication. The influences of the
various alcohol modifiers (in hexane-based mobile phase) on the structure and chiral
selectivity of the CSP were studied and compared. CPMAS spectra of Chiralpak AD flushed
with the mobile phases displayed clear evidence of solvent incorporation into the
CSP. When alcohol modifiers with varying size and bulkiness were used in the mobile
phase, differences in structure and chiral selectivity were observed on Chiralpak
AD based on solid-state NMR and chromatographic data. The change of t-butanol concentration
in the t-butanol/hexane mobile phase caused changes of structure and chiral selectivity
of the Chiralpak AD. These data further support our belief that the different chiral
selectivities of the CSP associated with the use of different alcohol modifiers are
due to different alterations of the steric environment of the chiral cavities in the
CSP by the different mobile-phase modifiers.